The piezoelectric effect is a reversible process whereby certain materials may internally generate electrical charge resulting from an applied mechanical force, or inversely generate mechanical strain resulting from an applied electric field. Piezoelectric materials may be used to form devices such as actuators, sensors, and motors. Traditional macroscopic piezoelectric devices utilize “bulk” piezoelectric material that because of large thicknesses, typically require large operating voltages in actuator applications. The same devices have increased versatility as the piezoelectric material and corresponding device structure are implemented in smaller form factors. Currently, one of the smallest developed implementations is through the use of microelectromechanical systems, microelectromechanical machines, or micromachines (generally referred to as MEMS) technology. MEMS can exploit the properties of thin film piezoelectric material to miniaturize piezoelectric devices. In contrast to bulk piezoelectric material, thin film piezoelectric material can be operated at very small voltages and the very thin structures that can be realized in MEMS allow for much larger displacements relative to the size of the actuator than with bulk piezoelectrics.
The piezoelectric MEMS technology is, however, limited when it is desired to form more than one piezoelectric thin film layer on the same substrate. FIG. 1 is an illustration of a conventional piezoelectric deposition comprising a silicon substrate 100, silicon dioxide layer 105, and metal layers (1151, 1152, and 115n hereinafter referred to as 115) on opposite sides of piezoelectric material layers (1101 and 110n hereinafter 110). The fabrication technique includes the deposition on a substrate 100 (such as silicon) and insulator 105 (e.g. silicon dioxide) of alternating two dimensional layers of metal 115 and piezoelectric material 110 of varying size, stacked on top of the same substrate 100. The ratio of the thickness of the piezoelectric layer to the thickness of the substrate is typically quite small, such as 1/300 or less. The aforementioned vertical stacking of such two dimensional structures limits the realization of a large volume of thin film piezoelectric material per unit area of the silicon substrate 100, as each subsequent piezoelectric layer 110 requires additional deposition and possibly additional etching fabrication stages.
For example, obtaining a conventional device comprised of 50 piezoelectric layers (110) may require the deposition of 50 piezoelectric layers (110), and 100 layers of metal (115). Thus, it becomes difficult to obtain a large volume of thin film piezoelectric material per unit area of the same substrate without drastically increasing the number of material layers when using traditional methods.
Therefore, a method and apparatus is needed to effectively form multiple piezoelectric thin film structures on the same substrate while enabling device operation in a third dimension and conserving manufacturing cost.